The TSP requests a 'dynamic' port from the OS. The OS's port allocation logic and configurations control which port is actually returned. The TSP actually binds the port when the Wave Driver is initialize (this is part of the TSP initialization process). Each instance of the Wave device has a UDP port after the intialization is complete that it uses. Depending on which CTI Port you are using, it will use the corresponding Wave Device (and the corresponding port) for media.

It is not possible to restrict the port range returned by Windows via the TSP config or TAPI code.